Jeffty is Five by Harlan Ellison

Jeffty is Five by Harlan Ellison (F&SF, July 1977) opens with a short “things aren’t what they used to be” passage about Clark Bars (a period confectionary) before going on to give a nostalgic account of the narrator Donny Horton’s childhood years. During this, Horton talks about a young boy called Jeffty:

When I was that age, five years old, I was sent away to my Aunt Patricia’s home in Buffalo, New York for two years.
[. . .]
When I was seven, I came back home and went to find Jeffty, so we could play together.
I was seven. Jeffty was still five.
I didn’t notice any difference. I didn’t know: I was only seven.
[. . .]
When I was ten, my grandfather died of old age and I was “a troublesome kid,” and they sent me off to military school, so I could be “taken in hand.”
I came back when I was fourteen. Jeffty was still five.
[. . .]
At eighteen, I went to college.
Jeffty was still five. I came back during the summers, to work at my Uncle Joe’s jewelry store. Jeffty hadn’t changed. Now I knew there was something different about him, something wrong, something weird. Jeffty was still five years old, not a day older.
At twenty-two I came home for keeps. To open a Sony television franchise in town, the first one. I saw Jeffty from time to time. He was five.  p. 9-10

After Horton settles back into town he occasionally takes Jeffty out to the movies, etc., and recounts the awkward visits to his house afterwards, where the parents are obviously troubled by their strange son:

“I don’t know what to do any more,” Leona said. She began crying. “There’s no change, not one day of peace.”
Her husband managed to drag himself out of the old easy chair and went to her. He bent and tried to soothe her, but it was clear from the graceless way in which he touched her graying hair that the ability to be compassionate had been stunned in him. “Shhh, Leona, it’s all right. Shhh.” But she continued crying. Her hands scraped gently at the antimacassars on the arms of the chair.
Then she said, “Sometimes I wish he had been stillborn.”
John looked up into the corners of the room. For the nameless shadows that were always watching him? Was it God he was seeking in those spaces? “You don’t mean that,” he said to her, softly, pathetically, urging her with body tension and trembling in his voice to recant before God took notice of the terrible thought. But she meant it; she meant it very much.  p. 15

The story’s major development occurs when Horton finds Jeffty in his den under the porch and sees what looks like a brand new Captain Midnight Secret Decoder Badge (not made since 1956). Jeffty tells Horton that it arrived in the mail that day and, when pressed further, says that he ordered the ring so he could decode the message on the next Captain Midnight radio show (not transmitted after 1950). When Horton asks to listen to the show, Jeffty points out that it isn’t on that night (it is the weekend), so Horton returns a few days later:

He was listening to the American Broadcasting Company, 790 kilocycles, and he was hearing Tennessee Jed, one of my most favorite programs from the Forties, a western adventure I had not heard in twenty years, because it had not existed for twenty years.
I sat down on the top step of the stairs, there in the upstairs hall of the Kinzer home, and I listened to the show. It wasn’t a rerun of an old program, because there were occasional references in the body of the drama to current cultural and technological developments, and phrases that had not existed in common usage in the Forties: aerosol spray cans, laseracing of tattoos, Tanzania, the word “uptight.”
I could not ignore the fact. Jeffty was listening to a new segment of Tennessee Jed. pp. 18-19

When Horton checks his car radio he can’t pick up the program, and realises that Jeffty is not only not aging, but seems to live in a world that is largely like his childhood one (with the minor contemporary changes mentioned above).
Horton spends the next part of the story experiencing life in Jeffty’s world: he hears a number of radio programs from his youth, Terry and the Pirates,1 Superman, Tom Mix, etc.; he goes to the movies to see Humphrey Bogart in Slayground (a movie of a Donald Westlake novel that was never made); he eats and drinks the products of the time (Quaker Puffed Wheat Sparkies); and—perhaps the only part of this world that particularly resonated with me—he sees new issues of pulp SF magazines:

Twice a month we went down to the newsstand and bought the current pulp issues of The Shadow, Doc Savage and Startling Stories. Jeffty and I sat together and I read to him from the magazines. He particularly liked the new short novel by Henry Kuttner, “The Dreams of Achilles,” and the new Stanley G. Weinbaum series of short stories set in the subatomic particle universe of Redurna. In September we enjoyed the first installment of the new Robert E. Howard Conan novel, ISLE OF THE BLACK ONES, in Weird Tales; and in August were only mildly disappointed by Edgar Rice Burroughs’ fourth novella in the Jupiter series featuring John Carter of Barsoom—“Corsairs of Jupiter.” But the editor of Argosy All-Story Weekly promised there would be two more stories in the series, and it was such an unexpected revelation for Jeffty and me, that it dimmed our disappointment at the lessened quality of the current story.  p. 21

(Robert E. Howard was already long dead by the 1950s, so I’m not sure how he is still alive in Jeffty’s world—one of the inconsistencies of this piece, along with the anomalous intrusions of the present day.)
Horton (spoiler) experiences the best of both worlds for a while (he still lives in the “normal” world while being able to savour Jeffty’s) but, of course, this charmed existence eventually slips through his hands on the day they go to the cinema to see The Demolished Man. The pair detour via Horton’s Sony store and find it so busy that Horton has to help out, and Jeffty is parked in front of thirty-three TVs showing modern shows. After some time Horton checks on Jeffty and sees that he looks unwell (“I should have known better. I should have understood about the present and the way it kills the past”). Horton gets him away from the TVs by telling Jeffty to go on to the cinema while Horton attends to a final customer. However, while Jeffty is queueing for the movie, he is beaten up by two youths after he borrows a radio and leaves it stuck in his world.
Horton takes the badly injured Jeffty home, and then, in an ending that is not as clear as it could be, Jeffty dies of his injuries.2
This story won that year’s Hugo and Nebula Awards, and I think I can see why: Ellison was, at that point in time, at the top of his game (in my opinion the period from the mid-60s to the mid-70s) and very popular; the story was from a special author issue of F&SF; and, finally, the subject matter would have been hugely appealing to those of a similar generation who were nostalgic for their lost pasts.3
Personally, I liked the story well enough, but I wouldn’t say it is the strongest of his tales for a number of reasons: while the gimmick is a neat one, the ending is weak and somewhat contrived (the TV set route would have been a better way to go); it could do with another draft (it is a little too long, and some of the sentences sound odd, e.g., “the ability to be compassionate had been stunned in him” from the passage above just sounds clumsy);4 the couple’s dislike of their own child is unconvincing (most parents seem to love their children regardless of their infirmities and shortcomings); and, finally, I am not a huge fan of nostalgia (insert your own “it ain’t what it used to be” joke here).5
So, overall, this classic is a good story, but not a great one (although it impressed me more on first reading).
*** (Good). 8,200 words. Story link.

1. You can find old Terry and the Pirates radio programs on the Internet Archive. I wouldn’t bother.

2. According to Wikipedia and other sources the mother drowns Jeffty in the bath at the end of the story—that is not clear from the text (and goes to my comment about the piece needing another draft).

3. The story’s nostalgia for the past comes along with a distinct antipathy for the present:

Today, I turn on my car radio and go from one end of the dial to the other and all I get is 100 strings orchestras, banal housewives and insipid truckers discussing their kinky sex lives with arrogant talk show hosts, country and western drivel and rock music so loud it hurts my ears.  p. 10

Things are better in a lot of ways. People don’t die from some of the old diseases any more. Cars go faster and get you there more quickly on better roads. Shirts are softer and silkier. We have paperback books even though they cost as much as a good hardcover used to. When I’m running short in the bank I can live off credit cards till things even out. But I still think we’ve lost a lot of good stuff. Did you know you can’t buy linoleum any more, only vinyl floor covering? There’s no such thing as oilcloth any more; you’ll never again smell that special, sweet smell from your grandmother’s kitchen. Furniture isn’t made to last thirty years or longer because they took a survey and found that young homemakers like to throw their furniture out and bring in all new color-coded borax every seven years. Records don’t feel right; they’re not thick and solid like the old ones, they’re thin and you can bend them . . . that doesn’t seem right to me. Restaurants don’t serve cream in pitchers any more, just that artificial glop in little plastic tubs, and one is never enough to get coffee the right color. Everywhere you go, all the towns look the same with Burger Kings and MacDonald’s and 7-Elevens and motels and shopping centers.
Things may be better, but why do I keep thinking about the past.

I don’t think the narrator is nostalgic for the past, but for an idealised version of it—cherry picking the things he likes and largely ignoring those that were also of that time: racism, sexual discrimination, possible nuclear oblivion (the list is long).
I’d also note that this reactionary nostalgia is a not uncommon trait in some SF fans. Although they spend a good chunk of their time reading about imagined futures, some have a pronounced dislike of modern technology: I’ve lost count of the number I have come across who actively dislike ebooks, smartphones, etc.; who shun streaming services in favour of DVDs; use chequebooks rather than credit/debit cards or Paypal, and so on.

4. Further to my comments about the story needing another draft, the introduction states that the story arrived “in [. . .] an impressive envelope from something called Federal Express Courier-Pak. It screams RUSH /URGENT from every corner”.
It’s also worth reading Joanna Russ’s F&SF (February 1979) review about the writing in this story.

5. My corrective for those suffering from too much nostalgia—Malcolm Jameson’s Blind Alley.